Electrophotographic printers have been known and used in various fields. Typically, such a printer accommodates a photosensitive drum and a developing roller. To print an image on a recording medium, an electrostatic latent image is formed on the photosensitive drum. The developing roller is held in pressure contact with the photosensitive drum to supply toner to the photosensitive drum and develop the electrostatic latent image with the toner. The toner image is transferred onto and thermally fixed on the recording medium.
When the printer of the typed described above is shipped while holding the developing roller in pressure contact with the photosensitive roller, the developing roller may be deformed during transportation or movement to the custody. When the printer with the deformed developing roller is used for printing by an end user, the printed image would be defective.
Japanese Patent Application Publication No. 2002-40905 discloses a mechanism for temporarily separating the developing roller from the photosensitive drum. In the printer disclosed in Japanese Patent Application Publication No. 2002-40905, a process cartridge is mounted in the printer body. The process cartridge includes a drum unit and a developing unit, in which both units are combined to form the process cartridge and normally held in an urged state. The outer wall of the drum unit is formed with a hole, and the outer wall of the developing unit with a dowel extending into the hole of the drum unit to engage therewith. The engagement of the dowel with the hole restricts the movements of the developing unit relative to the drum unit, and the developing roller can be held in spaced-apart from the photosensitive drum.
The dowel-hole engagement mechanism is configured to disengage the dowel from the hole when the process cartridge is mounted in the printer body. The process cartridge needs to be pushed into the printer body to mount it therein with stronger pushing force than force required to mount a process cartridge with no dowel-hole engagement mechanism. In other words, with the process cartridge having the dowel-hole engagement mechanism, additional force is needed to disengage the dowel from the hole. As the stronger pushing force is needed, it may be difficult for a certain user to mount the process cartridge in the printer body.
When the dowel-hole engagement mechanism disclosed in Japanese Patent Application Publication No. 2002-40905 is applied to a color printer having a plurality of process cartridges corresponding to a plurality of colors of toner, the user is imposed upon far more difficulty in mounting the plurality of process cartridges in the color printer body. The difficulty may invite such a problem that disengagement of the dowel from the hole is not accomplished during mounting of the process cartridges. If such a problem occurs, printing cannot be performed even if the process cartridges are believed to be properly mounted in the color printer.